An example of a conventional vibration gyroscope is illustrated in FIG. 18. In this vibration gyroscope, piezo-electric elements 2 and 3, which form vibrator 4, are respectively connected via the impedance elements Z1 and Z2 to the output side of a drive apparatus 6. The output side of the drive apparatus 6 is also connected, via another impedance element Z3, to a capacitor C, so that drive signals from the drive apparatus 6 are simultaneously applied to the piezo-electric elements 2 and 3 and on the capacitor C.
The outputs at the respective nodes of impedance elements Z1 and Z2 and piezo-electric elements 2 and 3 are combined. This combined output and the output at the nodes of impedance element Z3 and capacitor C are supplied to differential amplifier 7. The differential output is fed back to drive apparatus 6 so that vibrator 4 self-oscillates. The outputs at the respective nodes of impedance elements Z1 and Z2 and piezo-electric elements 2 and 3 are supplied to another differential amplifier 8, so as to obtain an angular velocity detection signal based on the output from the differential amplifier 8.
An example Of a vibrator 4, shown in FIG. 19, has a square cross sectional shape and has piezo-electric element 2 on one side surface 1a of vibration member 1 having a resonance point and piezo-electric element 3 on another side surface 1b adjoining the first side surface 1a. Another example of a vibrator 4, shown in FIG. 20, has piezo-electric elements 2 and 3 split in the wide direction on the same side of vibration member 1. Another example of a vibrator 4, shown in FIG. 21, has piezo-electric elements 2 and 3 on opposite sides of vibration member 1. Another example of a vibrator 4, shown in FIG. 22, has the respective piezo-electric elements 2a and 2b on opposite side surfaces of vibration member 1 and connects them in parallel so that they also act essentially as one piezo-electric element 2 and also has the respective piezo-electric elements 3a and 3b on the other opposite sides so as to connect them in parallel so that they act essentially as one piezo-electric element 3.
Still another example of a vibrator 4, shown in FIG. 23, has a triangular cross-sectional shape and piezo-electric elements 2 and 3 on two side surfaces of vibration member 1 having a resonance point. Another example of a vibrator 4, as shown in FIG. 24, has a circular cross-sectional shape and piezo-electric elements 2 and 3 on the peripheral surface of vibrator member 1 having a resonance point. Thus, members having essentially two piezo-electric elements are formed on the side surfaces of vibration members having various sectional shapes.
FIG. 26 shows a vibrator 4 with a single piezo-electric element 5 formed on vibration member 1, as shown in FIG. 25. FIG. 27 shows a vibrator 4 having two piezo-electric elements 2 and 3, is as shown in FIGS. 19 through 24.
However, the conventional vibration gyroscope shown in FIG. 18 is made so that it applies the drive signals from drive apparatus 6 to piezo-electric elements 2 and 3 via impedance elements Z1 and Z2. Therefore, the signal level applied to piezo-electric elements 2 and 3 decreases when the impedances of piezo-electric elements 2 and 3 decrease in the vicinity of the mechanical series resonance frequency f.sub.s in vibrator 4. The frequency at which the output from differential amplifier 7 is at a maximum and the mechanical series resonance frequency f.sub.s do not coincide. This phenomenon will be explained next, with reference to FIG. 28 and FIG. 29.
FIGS. 28A and B illustrate measurement examples of the frequency and phase characteristics of admittance .vertline.Y.vertline. of vibrator of the construction shown in FIG. 19. FIGS. 29A and B show the transfer and phase characteristics of differential amplifier 7. The vibration gyroscope illustrated in FIG. 18 connects piezo-electric elements 2 and 3 directly to the respective impedances Z1 and Z2, so that, as will be understood from FIG. 28A, the signal levels applied to these piezo-electric elements 2 and 3 decrease in the vicinity of the mechanical series resonance frequency f.sub.s where .vertline.Y.vertline. is large and increase in the vicinity of the mechanical parallel resonance frequency f.sub.a where .vertline.Y.vertline. is small. Therefore, the output of differential amplifier 7 receives the effect of the mechanical parallel resonance frequency f.sub.a with its high signal level. The maximum value frequency shifts to the mechanical parallel resonance frequency f.sub.a, as shown in FIG. 29A.
Vibrator 4, as indicated by the equivalent circuit in FIG. 30, is represented with regard to one piezo-electric element as a parallel resonance circuit where damping capacity Cd is connected in parallel to the series resonance circuit comprising inductor coil L1, capacitor C1 and resistance R1. Resistances and capacitors, for example, are used for impedance elements Z1 and Z2. When capacitors are used as impedance elements Z1 and Z2, the impressed signals also create phase changes determined by the value of damping capacity Cd relative to the resistance values of impedance elements Z1 and Z2. Therefore, the levels and phases of the applied signals vary in a complex fashion with the impedance changes in vibrator 4 and the frequency where the output of differential amplifier 7 is at maximum goes to the mechanical parallel resonance frequency f.sub.a.
Furthermore, the equivalent constants of vibrator 4, i.e., damping capacity Cd, inductor L1, capacitor C1 and resistance R1, have individual temperature dependencies. Therefore, the frequencies where the output of differential amplifier 7 is at a maximum will vary under variations of ambient temperature. Since self-oscillating vibration occurs at frequencies where the output of differential amplifier 7 is at a maximum, variations in set frequencies of self-oscillating vibration are easily brought about by variations in ambient temperatures.
The mechanical quality coefficient Q.sub.m of vibrator 4 is such that there will be no accurate agreement between the values on the piezo-electric element 2 side and the values on the piezo-electric element 3 side, so that fluctuations in the set frequencies of self-oscillating vibration bring about differences in the outputs of impedance elements Z1 and Z2 and the nodes of piezo-electric elements 2 and 3, so that low voltages and fluctuations tend to occur.
Furthermore, vibrator 4 has impedance elements Z1 and Z2 connected to piezo-electric elements 2 and 3 which leads to high impedance overall. The effects of electrical noise tend to occur at the respective nodes of piezo-electric elements 2 and 3 and impedance elements Z1 and Z2.